La2o3-tio2-ta2o5-zro2-bao-b2o3-sio2 optical glass



United States Patent Int. Cl. C031: 3/08 U.S. Cl. 10654 10 Claims ABSTRACT OF THE DISCLOSURE An optical glass composition which is productive of a glass exhibiting high resistance to thermal crystallization and which is tailored to provide in conjunction therewith such additional physical properties as chemical durability, a coefiicient of thermal expansion of from 80 to 100x 10 in the temperature range of 0-425 C., and an index of refraction (113) of from 1.77 to 1.90. The glass composition consists of at least seven essential oxides which together constitute not less than 64% by weight of the total composition. The seven essential oxides on a theoretical oxide basis are La O TiO BaO, B 0 SiO Ta O and ZrO which with other specific beneficial, but non-essential, oxide constituents are present together in the following relative ranges of percents by weight:

The present invention pertains to novel glass compositions and, more particularly, to optical glasses possessing highly desirable physical properties.

Optical glasses are generally employed by industry and science for many purposes. Among the purposes for which optical glass compositions are employed are mosaics for image intensifier tubes, the manufacture of fiber optics, optical computers, flexible fiber optic cystoscopes, cathoderay face plates and the like. Other purposes that use optical glass compositions are items of commerce such as lens, instruments for research and general laboratory work, astronomical disks and the like. The optical glasses used for the above-mentioned purposes should exhibit stable characteristics, such as being essentially free from devitrification for, in the manufacture of fiber optic systems, as mentioned in the former group of purposes, it is often necessary to reheat and reform the optical glass before the final product is effected. In the fabrication of the items of commerce, as mentioned in the latter group of purposes, the optical glass item is often subjected to the slight thermal effects produced by grinding, regrinding, polishing and repolishing as may be necessary to effect the desired final product. Also, the optical glasses used for the above-mentioned purposes require a glass composition with good chemical durability for acids and alkali, they must also possess physical and chemical homogeneity and a high order of freedom from imperfections like cords, strains, seeds, bubbles and the like. The optical glass composition should also possess a desirable index 3,513,004 Patented May 19, 1970 of refraction and good working characteristics for the fabrication of said scientific and industrial equipment. For some scientific or commercial application, such as in image intensifier systems, a desirable index is of import, as the higher the index of refraction, the greater the figure of merit.

Attempts have been made by the prior art to produce optical glass compositions with desirable characteristics as disclosed, for example, in US. Pat. Re. 21,175 and 2,206,- 081. However, certain of the compositions of Re'. 21,175 as reported in U.S. Pat. 3,150,990 are unstable and they tend to have a relatively high dispersion and a yellowbrown color. Other prior art attempts to produce optical glass involved the use of thorium, but, thorium is radioactive and the manufacture of glasses containing this element may therefore involve exposures to health-hazards. Still other attempts to effect optical glasses have involved the application of considerable amounts of rare earths, but, the optical glasses made in this fashion incline toward unstability as exemplified by devitrification.

It will be appreciated by those versed in the art that if optical glass compositions are compounded that are essentially very stable for reheating and reforming processes as employed for the manufacture of fiber optic systems, such optical glass would represent a useful contribution to the art. Likewise, it will be further appreciated by those skilled in the art that if optical glasses are compounded essentially-free from radioactive substances, with a high order of freedom from imperfections and with a desirable index of refraction, said optical glasses Would have a definite commercial value and a positive use for industry and science.

Accordingly, it is an object of the present invention to provide novel optical glass compositions.

Another object of the present invention is to provide optical glass compositions suitable for the manufacture of commercial and scientific ware.

A further object of the present invention is to provide optical glass compositions that are essentially free from seeds, cords, blisters and the like.

A still further object of the instant invention is to pro vide optical glasses that are essentially very stable for the fabrication and manufacture of optical fibers which can be subsequently sintered into a vacuum tight array.

A still further object of the present invention is to provide optical glasses that are essentially very stable for re heating and reforming for the manufacture of fiber optic core billets which can be subsequently fabricated into a flexible fiber optic system or sintered into a rigid vacuum tight array.

Yet a still further object of the present invention is to provide an optical glass with a high index of refraction.

Another object of the present invention is to provide an optical glass with a high index of refraction While maintaining the desired stable characteristics of the optical glass compositions and said glass being essentially-free from devitrification and essentially-free from crystallization and wherein said glass possesses desirable characteristics for fabrication into fiber optics and the like by conventional forming techniques.

Yet a further object of the present invention is to provide glass compositions that are essentially free from thorium and other radioactive substances while still maintaining a high index of refraction.

These and other objects and advantages of the invention will become apparent to those skilled in the art from the following detailed description and the accompanying claims.

In obtaining the novel optical glasses of the instant invention, it has now been found that optical glasses with a high. refractive index and essentially free from imperfections can be made by intimately blending various amounts of alkali, alkaline earth, rare earth and other oxides into an optical glass possessing optical homogeneity. The present invention provides optical glasses comprising about 5 to about 15 weight percent SiO about 7 to about 15 weight percent B about 0 to about 4 weight percent CaO, about 22 to about 30 weight percent BaO, about 2 to about weight percent Ta O about 18 to about 29 weight percent La O about 8 to about 14 weight percent TiO about 2 to about 9 weight percent ZrO about 0 to about 4 weight percent K 0, about 0 to about 4 weight percent Na O, about 0 to about 4 weight percent A1 0 and about 0 to 1.0 weight percent Li O; an optical glass comprising about 5 to about 15 weight percent SiO about 7 to about 15 weight percent B 0 about 0 to about 4 Weight percent CaO, about 22 to about 30 weight percent BaO, about 2 to about 5 Weight percent Ta O about 18 to about 29 weight percent La O about 8 to about 14 weight percent TiO about 2 to about 9 weight percent ZrO about 0 to about 4 weight percent K 0, about 0 to about 4 weight percent Na O, about 0 to about 4 Weight percent A1 0 about 0 to about 1.0 weight percent Li O, about 1 to about 5 weight percent Nb O and about 1 to about 10 weight percent W0 and a glass composition comprising about 5 to weight percent SiO about 7 to about 15 weight percent B 0 about 0 to about 4 weight percent CaO, about 22 to about 30 weight percent BaO, about 2 to about 5 weight percent Ta O about 18 to about 29 Weight percent La O about 8 to about 14 weight percent TiO about 2 to about 9 weight percent ZrO about 1 to about 5 weight percent Nb O about 0 to about 10 weight percent W0 and about 0 to about 1 weight percent Li O.

Exemplary of optical glass compositions according to the mode and manner of the present invention are an optical glass comprising about 14 weight percent SiO about 11 Weight percent B 0 about 2 weight percent CaO, about 29 weight percent BaO, about 3 weight percent Ta O about 22 weight percent La O- about 9 weight percent TiO about 6 weight percent ZrO about 1 weight percent Al O about 0.2 weight percent Li -O, and about 3 Weight percent K 0; an optical glass comprising about 8 weight percent SiO about 11 weight percent B 0 about 2.00 Weight percent CaO, about 29 weight percent BaO, about 4 weight percent Ta O about 23 weight percent La O about 12 weight percent T iO about 5 weight percent ZrO about 3 weight percent Nb -O and about 3 weight percent W0 an optical glass composition comprising about 8 weight percent SiO about 11 weight percent B O about 29 Weight percent BaO, about 5 Weight percent Ta O about 24 weight percent La O about 12 weight percent TiO about 3 weight percent ZrO about 5 weight percent W0 and about 3 weight percent Nb O Other optical glass compositions exemplary of subject glasses are glasses comprising about 8 weight percent SiO about 11 weight percent B 0 about 1 weight percent CaO, about 29 weight percent BaO, about 4 weight percent Ta O about 24 weight percent La O about 12 weight percent TiO about 5 weight percent ZrO about 3 weight percent Nb O and about 3 weight percent W0 an optical glass comprising about 8 weight percent SiO about 11 weight percent B 0 about 29 weight percent BaO, about 5 weight percent Ta 'O about 24 weight percent La O about 12 weight percent Ti02, about 8 weight percent ZrO and about 3 weight percent Nb O an optical glass comprising "8 weight percent SiO about 11 weight percent B 0 about 29 weight percent BaO, about 5 weight percent Ta O about 24 weight percent La O about 11 weight percent Ti02, about 8 weight percent ZrO about 1 weight percent U 0, and about 3 weight percent Nb O and, an optical glass consisting of 8 weight percent SiO about 11 weight percent B 0 about 2 weight percent CaO, about 29 Weight percent BaO, about 3 weight percent Ta O about 24 weight percent La O about 12 weight percent TiO about 8 weight percent ZrO and about 3 weight percent Nb O In preparing glasses of the above compositional ranges the batch ingredients are intimately mixed by hand or in a suitable blender and heated to such temperatures so that all substances are present in the liquidus state, and, thereby, enabling the formation of a glass with physical and chemical homogeneity from the homogeneous melt. Generally, the subject glasses thus formed have coefficients of thermal expansion of about to about l00 10" (0425 C.) with the now-preferred range of about to X 10' (0425 C.), and a refractive index for the D line of about 1.77 to about 1.90, with the nowpreferred range of about 1.77 to 1.80 and about 1.85 to 1.90.

The batch ingredients employed for the instant glass compositions are generally of the highest purity, and they are intimately mixed and then melted in a crucible. The crucible employed herein was platinum. The melting temperature for the subject compositions is generally in the range of about 2550 to about 2850 F. with the now generally employed range of about 2700 to about 2850 F. The crucibles were heated in an electric furnace and in an air atmosphere. The average glass melting time Was about 4 to about 8 hours, and the glass compositions were melted with constant stirring. Other glasses were prepared wherein the batch was melted over night, that is, for about 20 hours.

The commercially-available batch materials employed for preparing the glasses of the instant invention were of the highest purity and were generally selected from the following: Amersil sand, boric anhydride, calcium carbonate, barium carbonate, tantalum oxide, lanthanum oxide, titanium oxide, zirconium oxide, potassium carbonate, lithium carbonate, columbium oxide, tungstic acid and the like. While these are exemplary of the ingredients employed, other functionally equivalent reagents may be used for the glass compositions.

Batch constituents for preparing novel representative glasses of the instant invention are set forth in the table below, but these examples are not to be construed as limiting, as other suitable batch constituents for producing the glasses of the present invention may be employed within the manner and spirit of the invention.

The ingredients of the above examples were thoroughly blended and intimately melted in a platinum crucible at 2700 to 2 850 F. in an air atmosphere for about 7 to 8 hours. The theoretical composition, for the vitreous glass, expressed as percent by weight for the ingredients of Example 1, are set forth in Example 2.

In Table II, immediately below, is set forth the batch constituents, Example 3, and the theoretical composition, Example 4, for another optical glass prepared according to the instant invention.

[[n the tables set forth hereinafter, Table III and Table IV, are listed the theoretical composition and physical properties for novel optical glass compositions made according to the present invention.

TABLE III Theoretical composition Example 5 6 7 8 Ingredients:

SiOz 13. 43 13. 53 135 3 13. 53

Physical properties Fiber softening point, C 725 726 749 732 Annealing point, O 618 617 638 625 Strain point, C 588 588 608 597 Thermal expansion, X10- (0425 0.)-.- 95.4 95. 0 93. 9 95. 4

Index of refraction 1.7720 1- 7779 1- 7715 l. 7718 TABLE IV.-THEORETICAL COMPOSITION TABLE V.-CHEMICAL AND PHYSICAL PROPERTIES OF A FIBER OPTIC CORE GLASS Sim-13.53, Bios-11.06, CaO-2.14, BaO28.88, TazO3.27. L320.- 21.73, Tio.s.e7, ZrO26.02, K20- 3.30, 11120 -100, 1 120-4120.

Example Theoretical composition,

percent by weight.

Fiber softening point, C 731 73 733 728 Annealing point, C. 625 627 628 620 620 Strain point, C 508 599 600 588 588 Coefficient of expansion (0- 425 G 94. 1 e3. 5 93. 5 94. e 93. 3 Transmission in millimicrons'.

thickness in inches 1 1 1g 2. 2 3. 0 14. 1 26. 3 29. 2 47. 3 55. 4 64. 9 76. 5 78. 1 65. 3 72. 2 76. 2 82. 1 82. 2 81. 4 82. 3 84. 2 84. 9 85. 4 81. 4 81. 9 84. 1 84. 7 85. 3 84. 4 84. 4 85. 1 85. 7 86. l v 1. 7722 1. 7735 1. 7761 1. 7746 1. 7745 Melting temperature, F 2, 550 2, 600 2, 550 2, 650 2, 650 Melting time (hours). 20 5% 20 7% 7% The above-disclosed chemical and physical characteristics indicate that the subject glasses, generally essentially vitreous, have a fiber softening point of about 680 to 760 C., an annealing point of about 600 to about 670 C., a strain point of about 570 to about 640 C., a coef ficient of thermal expansion of about 80 to about 100 l0- (0425 C.) and a refractive index (ri of about 1.77 to about 1.90, which data appears to indicate the unexpected properties and unobvious qualities for the inventive glasses.

The novel optical glass compositions, when fabricated into rod form for cladding with an outer layer of a different glass, usually a borosilicate glass or a like glass or other suitable material, is cast or formed into rod form with a given external outside diameter that corresponds to the internal diameter of the cladding tubing. The cladding tubing with the fiber optic core billet positioned Percent by weight Example 9 10 11 12 13 14 15 Ingredients:

Physical Properties Fiber softening point, C 743 762 713 762 753 744 757 Annealing point, O. 654 661 622 654 656 656 664 Strain point, C 629 643 595 627 630 627 636 Index of refraction 1. 87 1. 86 1. 87 1. 87 1. 88 1. 87 1. 87

Glass compositions of the present invention were made into fiber optic core billets, and some of the fiber core billets were subsequently clad with a material of a lower index of refraction, said latter material being a borosilicate glass or the like or other suitable material. The cladded core billet was heated and drawn to reduce the diameter, and during and after this process the billet was essentially-free from devitrification. Next, the above product was reheated and redrawn to a smaller diameter. The reheating and redrawing steps can be repeated until the desired diameter for the fiber optic is obtained. The chemical and physical properties for an essentially vitreous fiber optic core glass made according to the present invention is set forth in the accompanying table, Table V.

therein is then heated and drawn into the desired fiber optic diameter. The cladding glass will have a refractive index which is lower than the optical core billet glass to perform successfully as a fiber optic system. The thermal expansion for the clad glass will usually be lower than the expansion of the subject glasses.

While the illustrative embodiments of the invention have been described with particularity, it will be understood that various modifications will be apparent and can readily be made by those skilled in the art without departing from the scope and spirit of the invention.

We claim:

1. An optical glass composition providing an index of refraction between about 1.7 7 and about 1.90 and consisting essentially of about 5 to about 15 weight percent S102,

about 7 to about 15 weight percent B about 0 to about 4 weight percent CaO, about 22 to about 30 weight percent BaO, about 2 to about percent weight percent Ta O about 18 to about 29 weight percent La O about 8 to about 14 weight percent TiO about 2 to about 9 weight percent ZrO together with about 0 to about 4 weight percent K 0, about 0 to about 4 weight percent Na O, about 0 to about 4 weight percent A1 0 and about 0 to about 1 weight percent Li O.

2. A glass composition, according to claim 1 containing about 14 weight percent SiO about 11 weight percent B O about 2 weight percent CaO, about 29 weight percent BaO, about 3 weight percent Ta O about 22 weight percent LaO, about 9 weight percent TiO about 6 weight percent ZrO about 1 Weight percent A1 0 about 0.2 weight percent U 0, and about 3 weight percent K 0.

3. An optical glass composition consisting essentially of about 5 to about 15 weight percent SiO about 7 to about 15 weight percent B 0 about 0 to about 4 weight 4. An optical glass composition, according to claim 3,

containing about 8 weight percent SiO about 11 weight percent B 0 about 2 weight percent CaO, about 29 weight percent BaO, about 4 weight percent Ta O about 23 weight percent La O about 12 weight percent T iO about 5 weight percent ZrO about 3 weight percent Nb O and about 3 weight percent W0 5. An optical glass composition, according to claim 3, containing about 8 weight percent SiO about 11 Weight percent B 0 about 29 weight percent BaO, about 5 weight percent Ta O about 24 weight percent La O about 12 weight percent TiO about 3 weight percent ZrO about 5 weight percent W0 and about 3 weight percent Nb O 6. An optical glass composition, according to claim 3, containing about 8 weight percent SiO about 11 weight percent B 0 about 1 weight percent CaO, about 29 8 Weight percent BaO, about 4 weight percent Ta O about 24 weight percent La O about 12 weight percent TiO about 5 weight percent ZrO about 3 weight percent Nb O and about 3 Weight percent W0 7. An optical glass composition consisting essentially of about 5 to 15 weight percent SiO about 7 to about 15 Weight percent B 0 about 0 to about 4 Weight percent CaO, about 22 to about Weight percent BaO, about 2 to about 5 weight percent Ta O about 18 to about 29 weight percent La o about 8 to about 14 weight percent TiO about 2 to about 9 Weight percent ZrO together with about 0 to about 1 weight percent Li O, about 1 to about 5 weight percent Nb 0 and about 0 to about 10 weight percent W0 8. An optical glass composition, according to claim 7, containing about 8 weight percent SiO about 11 Weight percent B 0 about 29 weight percent BaO, about 5 weight percent Ta O about 24 weight percent La o about 12 weight percent TiO about 8 weight percent ZrO and about 3 weight percent Nb O 9. An optical glass composition, according to claim 7, containing about 8 weight percent SiO about 11 weight percent B 0 about 29 weight percent BaO, about 5 Weight percent Ta O about 24 Weight percent La o about 11 Weight percent TiO about 8 weight percent ZrO and about 1 weight percent U 0 and about 3 weight percent Nb O 10. An optical glass composition, according to claim 7, containing about 8 weight percent SiO about 11 weight percent B 0 about 2 weight percent CaO, about 29 weight percent BaO, about 3 weight percent Ta O about 24 weight percent La O about 12 Weight percent TiO about 8 weight percent ZrO and about 3 Weight percent Nb O References Cited UNITED STATES PATENTS 2,576,521 11/1951 Kreidl et a1 10654 FOREIGN PATENTS 1,020,795 2/ 1966 Great Britain. 725,206 3/ 1955 Great Britain. 974,438 1 1/ 1964 Great Britain.

JAMES E. POER, Primary Examiner UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3, 513, 004 DATED y 1970 INVENTOR(S) 1 Jaroslaw Kohut, et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 4, line 27, after "commercially", delete hyphen Col. 5, Table 3, Ext. 7, Si0 Content "135.3" should be l3.53; Table 4, Ex. 10, under Annealing Point Physical Properties "661" should be -67l. Col. 7. line 14. "Leo" should be --La O Signed and Scaled this twenty-seventh D y of January 1976 [SEAL] A nest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer (ummissr'uner nfParenrs and Trademarks 

